Has anyone gotten a good oscilloscope look at the type of signals
that distort by cancellation of part of the carrier, i.e. the
signals that synchronous detectors detect much better than other
types? I'm wondering about the characteristics that make these
signals so hard to understand when they "fade" into that condition.

--
All relevant people are pertinent.
All rude people are impertinent.
Therefore, no rude people are relevant.
-- Solomon W. Golomb